The main purpose for the device according to the invention is to control the flow through the valve so that in a real operational case a flow is obtained and an output power from the system corresponds to the demand that has to be fulfilled, and this in such a way that no problem with sound or power control will arise.
Both those variables are coupled to the static pressure level and to the fall of pressure existing in the medium that the complete valve has to control.
Because the control valve has to fulfill its function at varying system conditions the valve is carried out as a combination of a flow control valve and a differential pressure valve. The differential pressure valve limits the differential pressure—the Δp-value—to which the control valve is exposed. Because the Δp-value is limited to a selected value, for example 10 kPa, and since this value additionally is more or less constant, independent of variations of the pressure level in the entire system, the best conditions for a good control function are obtained. Consequently the control valve can be dimensioned in an optimal way, which leads to that the system in which the control valve is working can be controlled so that for example a room temperature is held within selected values without fluctuations in temperature or that for instance sound problems occurs.